After Market Transmission Fluid

I just purchased a 2002 'pre-owned' Mini!!! Super excited, but previous owner did not take good care of it. I Need your help!

Is there an after-market transmission fluid that you guys would recommend, that is compatible with OEM fluids? I called BMW and they quoted me $250 for the fluid b/c they sell only bulk quantity; no one liter bottles. I appreciate your help.